Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF FUEL CELL SCIENCE AND TECHNOLOGY. Manuscript received September 6, 2012; final manuscript received December 20, 2012; published online June 10, 2013. Assoc. Editor: Umberto Desideri.

The increasing use of unattended sensors by the Information, Surveillance, and Reconnaissance community requires the development of higher power and energy density sources to provide increased capabilities and operation time while minimizing size and weight. Among the emerging power sources, fuel cell (FC) systems potentially offer an improved alternative to existing solutions. The Communications and Electronics Research and Development and Engineering Center/Command, Power & Integration Directorate/Army Power Division's Power Sources branch has been evaluating fuel cells to meet tactical power military applications. Testing of methanol based FC systems indicates 50% weight savings over a secondary Li-ion rechargeable system at 200 W h, and 30% weight savings over a primary Li battery at 600 W h. However, significant technical barriers to fuel cell based power sources for sensor deployment exist, including requirements for additional size and weight reduction to meet portable sensor design requirements. Additionally, testing of FC systems demonstrate the importance of appropriate battery hybridization to maintain load following as well as increasing system power density. A comparison of a Reformed Methanol FC system and a Direct Methanol FC system was also completed, and results for the system size, weight, and fuel consumption are similar for both technologies. To examine the benefits of larger power fuel cells appropriate for stationary unattended sensor use, a comparison of power and weight available from a solar/battery hybrid system versus a solar/battery/RMFC hybrid system was also completed. Although the solar/battery hybrid system's size and weight are larger than the hybrid system with an FC unit, 14 kg versus 8 kg, respectively, there is significant logistic burden when utilizing a FC system due to its methanol refueling requirement.

DMFC hybridized with a battery to provide 5× power increase. DMFC charges battery and shuts down when battery fully charged. Battery meets increased power requirements until it is depleted, when load is cut off and DMFC recharges battery.

Fuel cell system response to step load increase. When load is increased from 5 to 47 W, fuel cell system requires 100 s to reach new steady state value. System response limited by fuel processing subsystem.

RMFC/battery response to step load increase. To maximize lifetime, the FC system is limited to peak load changes >7 s. The use of an external 80 W h battery allows uninterrupted load following by the system.

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